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Topic: How to Test a Lens (Read 2613 times)

So this is a pointed question, but could certainly turn into a broader topic of lens testing.

So yesterday my brand new 70-200mm f/2.8L IS II USM arrived, and I couldn't have been more excited. I've been scoping it out for awhile, and finally pulled the proverbial trigger when I'd squirreled away enough money. I'd long heard about how amazingly sharp this lens is, and already owning two other L lenses, I definitely have the red ring addiction.

So I got home and decided to test the lens, since I've had some some copy issues with Sigma (I know, they don't have Canon's QA). I compared it to my primary lens, the 24-70mm f/2.8L. I took pictures of one of my wife's cookbooks at 70mm (obviously the only comparable focal length) at apertures f/2.8, f/8, f/11, and f/16. Camera (5Dm3) was tripod mounted, ISO set at 100, mirror locked, and shutter triggered by a two second delay.

I gotta say, I was a little surprised when the two lenses came out pretty close in terms of sharpness at 70mm at f/2.8. While the 70-200mm was a hair sharper, it wasn't the "omg the 70-200mm blows the 24-70mm out of the water" that I had expected. I wish I had comparison images to post, but unfortunately I left my camera at home, and wanted to post this topic while it was fresh in my head. I'll post the photos when I get home tonight.

So I have two questions:

1) I'm no professional, so does anyone who is or has experience with these lenses have any input? I'd heard the 24-70 was notoriously soft (never really noticed it myself), and expected the 70-200mm to be noticeably sharper. Bottom line, I'm concerned I may have gotten a soft copy of the 70-200mm, and at $2500, I'd likely get it replaced if that's the case.

2) Does anyone have a favorite method of testing lenses? I've often photographed a newspaper taped to a wall or something similar (cookbook) to check the center, corners, etc at various focal lengths and apertures. I'd love to get one of those testing charts, but they're wildly expensive online and I'd rather buy actual gear.

Already read that article, and I'm very familiar with the technical aspects of testing a lens.

Again, my question was a bit more pointed than that, and perhaps I shouldn't have titled the topic with such a vague subject. My question of emphasis was is there anyone here who can speak to sharpness of the 24-70mm f/2.8L compared to the 70-200mm f/2.8L IS II at 70mm? Mine seemed very close in sharpness/contrast, and I was a little surprised by that.

And my more generalized question was what are some of your favorite methods of testing a lens? I don't know a single photog that owns a lens resolution chart as mentioned in the article -- they're expensive, and every day items (news papers, wine bottles, etc) work almost as well. Are there any every day objects users here utilize to test resolution, contrast, colors, etc?

I'm sure others would find it interesting how casual photogs test their lenses.

Again, my question was a bit more pointed than that, and perhaps I shouldn't have titled the topic with such a vague subject. My question of emphasis was is there anyone here who can speak to sharpness of the 24-70mm f/2.8L compared to the 70-200mm f/2.8L IS II at 70mm? Mine seemed very close in sharpness/contrast, and I was a little surprised by that.

I don't have a 24-70 to compare to my 70-200 II, but I will point out tht TDP mentions testing 3 copies of the 70-200 II and finding one sharper at 70 than 200, the other two the reverse.

I always test lenses using everyday objects, but the again my demands aren't as exacting as possibly a professional's. I once downloaded and printed out the Edmund's chart, but found it unnecessary and cumbersome. I shoot indoors during daytime using filtered sunlight, with the camera on a tripod. I check for color fringing and front or back focusing at all apertures and both at the wide and tele end. I use a long steel ruler for the latter. Never owned the 24-70, although was blown away by the IQ of the 70-200 2.8 IS vII compared even to the 70-200 4 IS- totally subjective though, no technical comparisons. Bought the 70-200 2.8 IS vI since and can't be happier.

I can tell you with 100% certainty that a new out of the box lens won't always guarantee it is going to be spot on. I've brought two out of the box lenses to Canon for an alignment. After getting fed up with this, I got the Focal software which does a damn good job and worth it's weight in gold. It not only will assist with alignment but it will also tell you your lenses sharpest aperture (pro version). In addition, general rule of thumb (you may know this) is the 70 and the 200 focal points are probably the weakest (not saying they are bad). PS if you have a UV filter on try it without as it made a difference on my 400mm once removed.

I can tell you with 100% certainty that a new out of the box lens won't always guarantee it is going to be spot on. I've brought two out of the box lenses to Canon for an alignment. After getting fed up with this, I got the Focal software which does a damn good job and worth it's weight in gold. It not only will assist with alignment but it will also tell you your lenses sharpest aperture (pro version). In addition, general rule of thumb (you may know this) is the 70 and the 200 focal points are probably the weakest (not saying they are bad). PS if you have a UV filter on try it without as it made a difference on my 400mm once removed.

What focal software do you use? I might be interested in checking it out.

canon rumors FORUM

I use the software by Reikan called Focal. It's truly excellent. Be sure to thoroughly read all directions to get optimum results. of special note, put your metering on SPOT Metering. I write to the manufacturer and pointed this out that the software will not work properly unless Spot Metering is on amongst other things like covering the eye piece, use Live View Only, EV must be at 8 or higher so be sure there is plenty of light and so on.

I recall a site that had a 45% savings but apparently the link is no longer (just checked promo is over). You may want to search around and see if there are others.

Reikan FoCal will help set AFMA, I love it. Testing a lens / camera combination, which is what all the lens testers do, is a tricky proposition. The same lens mounted on seemingly identical cameras will give different results, and seemingly identical lenses when mounted on the same camera will give different results. All of them are likely meeting spec, but there are variations.I've seen a couple of testers note that the 24-70mm f/2.8 is not as sharp at the edges as its predecissor. but there is enough variation in lenses to require several more test results before we can see a definite trend.If the lens does not meet your expectations, return it for a second one.

So I swung by my favorite camera store this weekend and tested out another copy of the 70-200mm, and it seemed almost identical in sharpness compared to mine. So I'm hopefully just being paranoid. But since I'm an amateur/hobbiest, laying down that kind of money is a big deal to me. :-)

I did get some great pictures with it this weekend though. And I'm seriously considering the 2x extender for a trip to the Caribbean I have coming up in a few weeks. I know the extenders degrade quality a bit, but the possibility of having a 400mm lens in my bag is pretty hard to pass up... even at f/5.6.

I also have a 100mm f/2.8L macro that I'd like to use the extender on, but hear I would need an extension tube. Haven't been able to get a straight answer on the size of the tube needed though... anyone have experience with extenders and macro lenses?